Infusion devices and systems are relatively well known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact housing adapted to receive and support a reservoir carrying the prescribed medication for administration to the patient through infusion tubing and an associated catheter or the like. The infusion device includes a small drive motor connected via a lead screw assembly for motor-driven advancement of a reservoir piston plunger to deliver the medication to the patient. A programmable controller can be provided for operating the drive motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of medication over an extended period of time. Such infusion devices are utilized to administer insulin and other medications, with exemplary device constructions being shown and described in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653; 5,097,122; and 5,505,709, which are incorporated by reference herein.
Infusion devices of the general type described above have provided significant advantages and benefits with respect to accurate delivery of medication or other fluids over an extended period of time. The infusion device can be designed to be extremely compact as well as water resistant, and may thus be adapted to be carried by the user, for example, by means of a belt clip or the like. As a result, important medication can be delivered to the user with precision and in an automated manner, without significant restriction on the user's mobility or life-style.
These devices often incorporate a drive system that uses a lead screw coupled to motors. The motors can be of the DC, stepper or solenoid varieties. These drive systems provide an axial displacement of the reservoir or reservoir piston to dispense the medication to the user. Powered drive systems are advantageous since they can be electronically controlled to deliver a predetermined amount of medication.
FIG. 1 shows a lead screw arrangement that is known in the art. Located in a housing 107, a motor 101 drives a lead screw 102 that has threads, which are engaged with a drive nut 103. Thus, the rotational force of the lead screw 102 is transferred to the drive nut 103 that causes it to move in an axial direction d. Because the drive nut 103 is fixably attached to a reservoir piston 104, it likewise will be forced in an axial direction d′, parallel to direction d, thus dispensing the fluid from the reservoir 105 into the infusion set 106.
FIG. 2 shows a different lead screw arrangement that is also known in the art. In this arrangement, a motor 201 (or a motor with an attached gear box) has a drive shaft 201a that drives a set of gears 202. The torque is then transferred from the gears 202 to a lead screw 203. The threads of the lead screw 203 are engaged with threads [not shown] in a plunger slide 204. Thus, the torque of the lead screw 203 is transferred to the slide 204 which causes it to move in an axial direction d′, parallel to the drive shaft 201a of the motor 201. The slide 204 is in contact with a reservoir piston 205 which likewise will be forced to travel in the axial direction d′ thus dispensing fluid from the reservoir 206 into the infusion set 207. The assembly can be contained in a housing 208.
In the operation of these infusion device systems, the reservoir piston will be fully advanced when virtually all of the fluid in the reservoir has been dispensed. In certain infusion device mechanism (e.g. DC motor and/or stepper motor configurations), the axial displacement of a piston engagement with the motor lead screw (e.g. a nut) is also typically fully displaced when the reservoir is near empty. In these devices, to insert a new reservoir that is full of fluid, it is necessary to reverse the direction of the lead screw until the piston engagement returns back to the starting position. Thus, the drive system must be able to be reversed in direction. On the other hand, in solenoid based drive systems, the piston engagement must be reset manually when placing in a new full reservoir. Both types of reset methods are problematic. For example, in motor rewind configurations, the motor must be capable of being reversed requiring additional switches and more complex circuitry. In addition, home positioning “sensing” is required to shut off motor at home position, extra battery energy is consumed, such configurations do not accommodate a partially filled reservoir, etc. Similarly, manual reset configurations also have inherent problems. Typically, manual reset configurations require a more complex housing to accommodate an access to the lead screw/nut area (e.g. a hatch or a slot paralleling the lead screw). In addition, the disengageable nut is both difficult and costly to design and manufacture, the disengagement function must be safeguarded from any inadvertent actuation, additional wear issues must be considered, manual dexterity limits exist, etc.